1. Field of the Invention
The present invention relates to the field of medical instruments and more particularly to a surgical scalpel having an adjustable depth of cut.
2. Description of the Prior Art
Scalpels having adjustable depths of cut are used in many types of surgical procedures. In particular, an adjustable depth scalpel is useful in performing a surgical procedure known as radial keratotomy where radial cuts are formed in the outer surface of the eyeball. This procedure changes the curvature of the eyeball and alleviates the symptoms of myopia. Examples of scalpels designed to cut at adjustable depths are shown in U.S. Pat. Nos. 4,499,898 and 4,516,575.
Such a scalpel should allow a variable adjustment of the projection distance of the blade over a relatively wide range and include a convenient means for retracting and extending the blade. The retracted position is provided for protecting the blade when it is not in use while the variable adjustment is provided to control the depth of the incision.
It is desirable that the motions required to perform the extension, retraction and depth adjustment be simple and not allow unsatisfactory tolerances or movement of the blade to occur during use. To this end it is desirable that only one portion of the scalpel be required to turn or move to provide both the extension/retraction and variable depth functions. Prior art devices provide both extension/retraction and depth adjustment, but use combinations of movements and different scalpel portions to provide the respective extension/retraction or depth adjustment and control.
It is also desirable that the scalpel have a surface that provides maximum tactile feedback to the surgeon, allowing more accurate incisions to be made. The scalpel should also have a mechanism for maintaining a uniform depth of cut and yet allow maximum visibility of the knife blade at all times. The blade should also be firmly attached to the blade holder to prevent any inaccuracies due to blade wobble.
The incision depth is critical in many of the procedures using adjustable scalpels. Gauges to accurately set the blade depth in very fine graduations have been developed, as shown in U.S. Pat. No. 4,538,356. In the disclosed gauge, the scalpel is fixed in place and the disk rotated to align the depth marks with the blade. This gauge has the problem that the scalpel foot, the resting surface of the scalpel contacting the tissue, is in contact with the disk. When the disk is rotated, the two metal surfaces rub and an uneven finish appears on the foot, leading to possible scratches when the scalpel is used to make an incision.